Re: Synchronization Question
On Sat, 12 Sep 2009 13:34:44 -0700, Patricia Shanahan wrote:
If it is *never* actually read, why not get rid of it completely? The
fastest write is the one that does not get done at all.
I'm going to assume that the array is not read during the operation, but
is read after it is finished.
You're interpretation was correct. It isn't read until much later after
all the threads doing the update complete.
The JLS requires individual int writes to be atomic, so there is no
possibility of a mixed value from two different writes.
Well, that solves that problem.
The key question is exactly what you mean by "the last thread to update
it wins".
At the most flexible, it could merely mean that you want the final value
of each element to be one of the values written to it if it was written,
and the original value if it was never written. In that case, you just
need to make sure that each thread does something that causes its writes
to happen-before any read of the array. For example, any write by a
thread happens-before any read that follows a join that detects its
termination.
Great! So I don't need synchronization for this portion. Thanks!
If you really need to have the value come from the last thread to assign
to the array element, then you do need to synchronize each write.
I don't really care which value survives. I am in the "most flexible"
position described above.
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